1. Field of the Invention
The present invention relates to an improvement of a die used for sealing an electronic component such as an integrated circuit (IC) with resin to mold the same.
2. Description of the Background Art
Conventionally, a transfer mold method is employed to seal with resin an electronic component mounted for example to a lead frame, to mold the electronic component. This method uses a resin-sealing and molding die formed of a top, fixed die; and a bottom, movable die (hereinafter referred to as xe2x80x9ctop and bottom diesxe2x80x9d) and is typically conducted as described below:
The top and bottom dies are previously heated by heating means to have a temperature at which resin is molded, and the top and bottom dies are opened. Then, a lead frame with an electronic component mounted thereto is fed and set in the bottom die""s parting-line (P.L) plane (a die plane) at a predetermined position and a resin material is fed into a pot in the bottom die. Then, the bottom, movable die is moved upward and the both dies are closed, when the electronic component and the lead frame therearound are fit into upper and lower cavities respectively provided in the top and bottom dies on their respective one sides and facing each other and the resin material in the pot is heated and gradually melted. Then, the heated and melted resin material in the pot is introduced through a resin channel and thus injected into and fills the both of the upper and lower cavities and the electronic component and lead frame therearound in the upper and lower cavities are thus shielded with the resin and thus molded internal to a resin shielded body to correspond to the shape of the upper and lower cavities.
As such, after the passage of a period of time required for curing the melted resin material, the both dies are opened and an ejector pin provided in the both dies is employed to release the resin-molded body and lead frame in the upper and lower cavities and the resin cured in the resin channel.
The above, conventional die typically has a surface plated with hard chromium (HCr). As such, the upper and lower cavities both have a surface highly adhesive to a resin molded body. As such an ejector pin is not sufficient to eject and thus release the resin molded body from the cavities.
Furthermore, a resin molded body (a product) readily chips if an ejector pin is used to eject and thus release the resin molded body from the upper and lower cavities.
Furthermore, melted resin material readily enters the P.L plane of the dies and resin flash (the resin cured) remains and thus readily adheres. The adhering resin flash affects product size and the like and also enters the resin molded body to prevent uniform production of products.
Furthermore, if resin flash adheres to an air vent allowing the die cavity to externally communicate, the die cavity would be tightly sealed and cannot exhaust its internal air through the air vent. As such, the air in the die cavity is introduced into the resin molded body and the resin molded body would have a portion which is not filled with the resin.
Furthermore, to prevent resin flash from adhering a resin material is compounded with an increased amount of a mold release agent, although the mold release agent would degrade the adhesion between a surface of a lead frame made of metal and a resin molded body (the resin cured).
As such, there can hardly be obtained a high quality product (resin-molded body) that is highly reliable.
Furthermore, the die must have its surface frequently cleaned to remove resin flash remaining and thus adhering to the die surface. This would make the die surface cleaning difficult and time-consuming, resulting in an increased die molding cycle time.
Furthermore, in recent years with the necessity of changing to high-density surface-mounting, such mounting requires highly precise alignment and a product (a resin molded body) to be mounted is required to have a uniform size (a dimension with high precision). To provide the product with a uniform size, consideration is given to minimizing the contraction of a resin molded body when it is molded. For example, consideration is given to increasing the content of a filler such as hard powdery silica compounded in a resin material, to reduce the contraction thereof. In this technique, however, the hard powdery silica rapidly abrades the die surface and the die""s durability degrades and the die""s molding frequency also reduces. As such, the die must be replaced with a new die in a short period of time.
As such, the product is produced at a low level of productivity.
The present invention contemplates a die used for sealing an electronic component with resin to mold the electronic component, capable of improving the releaseability of a resin molded body with respect to the die to release the body from the die more efficiently.
The present invention also contemplates a die used for sealing an electronic component with resin to mold the electronic component, capable of providing a high quality product that is highly reliable.
The present invention also contemplates a die used for sealing an electronic component with resin to mold the electronic component, capable of enhancing the productivity for the product.
To achieve the above objects, the present invention provides the die used for sealing the electronic component with resin to mold the electronic component, having a coating layer of nickel-tungsten alloy on at least a surface thereof contacting a melted resin material when the resin is molded.
As such, there can be provided better releaseability of a resin-molded body with respect to the die to efficiently release the resin molded body.
The present invention in one embodiment provides the die used for sealing the electronic component with resin to mold the electronic component, wherein the coating layer is a plating layer formed of a nickel-tungsten alloy containing at least 20% by weight of tungsten.
The nickel-tungsten alloy (NiW) plating layer provided covering at least a surface contacting a melted resin material can provide better releaseability of a resin-molded body (or cured resin) than a surface processed by plating with hard chromium (HCr).
As such, the resin molded body can be efficiently ejected and released from the die cavities and the die can also be efficiently prevented from having resin flash (cured resin) adhering to its P.L plane or the like.
Furthermore, the surface provided with the NiW layer is greater in hardness than a surface processed with HCr. Thus, abrading and damaging the die can be minimized to enhance the durability of the die.
Consequently, the present invention can effectively provide a die used for sealing an electronic component with resin to mold the electronic component that is capable of providing a high-quality product that is highly reliable at a high level of productivity.
The present invention in one embodiment provides the coating layer (A) having a tungsten content of 20% by weight for the following reasons:
If a basic bathing of a nickel-tungsten alloy plating has a tungsten content below 20% by weight, e.g., 10% by weight, it would be a bathing which has a high temperature of 70 to 95xc2x0 C. and is ammonium-alkaline with pH 8 to 9. This high-temperature bathing contains ammonium significantly volatile and it can thus hardly be controlled. The ammonium also smells bad and thus degrades the working environment of interest.
Furthermore, if coating layer (A) has a tungsten content of approximately 10% by weight then electrolysis rapidly increases the layer""s electrostatic stress and also decreases the layer""s flexibility. This results in a crack in a surface of the coating layer.
Furthermore, while the nickel-tungsten alloy plating as it is has a hardness of approximately Hv. 600, this plating after being heated and thus cured can be as hard as Hv. 1350. In contrast, if a nickel-tungsten alloy plating with a tungsten content of approximately 10% by weight is heated and thus cured, it does not cure in separation and can only have a hardness of approximately Hv. 600, i.e. the same hardness of such a plating which has not been further processed.
Furthermore, a nickel-tungsten alloy plating containing no less than 20% by weight of tungsten is advantageous in that it is not corroded by concentrated hydrochloric acid, sulfuric acid, hydrofluoric acid, or nitric acid.
It should be noted, however, that tungsten is not separated from a solution with its ions existing independently and an induced eutectoid reaction occurs. To allow tungsten to be separated through such an induced eutectoid reaction, tungsten is contained with an upper limit of approximately 60% by weight. As such, coating layer (A) provided on the surface that a melted resin material contacts in sealing and molding, preferably has a tungsten content of no more than 60% by weight.
Furthermore, coating layer (A) is preferably 1 xcexcm to 20 xcexcm in thickness, since coating layer (A) exceeding 20 xcexcm in thickness has a spherical crystal and can thus not have a reliable surface and coating layer (A) less than 1 xcexcm in thickness is too thin to effectively plate a surface.
The present invention can be applied to a resin-sealing and molding die for example including a fixed die, a movable die arranged opposite to the fixed die, upper and lower cavities provided in the fixed die and the movable die in their respective die planes to face each other along a parting-line plane of the fixed die and the movable die, for molding the resin, a concavity receiving and setting a support having the electronic component mounted thereto, a pot arranged at one of the fixed die and the movable die for supplying the resin material, a plunger fit internal to the pot for applying pressure to the resin, and a resin channel to allow the pot and the upper cavity to communicate with each other for transporting the melted resin material, wherein the coating layer is provided on an internal surface of the upper and lower cavities, an internal surface of the resin channel, an internal surface of the concavity, an internal surface of the pot, the parting-line plane of each of the fixed die and the movable die, and an external surface of the plunger.
Furthermore, if the die further includes an ejector pin ejecting and releasing from the upper and lower cavities a resin-molded body molded in the upper and lower cavities and an ejector pin fitting hole fitting the ejector pin therein, preferably the ejector pin has an external surface provided with the coating layer of nickel-tungsten alloy and/or the ejector pin fitting hole has an internal surface provided with the coating layer of nickel-tungsten alloy.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.